Photographic elements relying on silver halide emulsion for image recording have been recognized to possess outstanding sensitivity to light for more than a century. Roentgen discovered X radiation by the inadvertent exposure of a silver halide photographic element. In 1913 the Eastman Kodak Company introduced its first product specifically intended to be exposed by X radiation.
The desirability of limiting patient exposure to high levels of X radiation has been recognized from the inception of medical radiography. In 1918 the Eastman Kodak Company introduced the first medical radiographic product which was dual coated-that is, coated with silver halide emulsion layers on the front and back of the support.
At the same time it was recognized that silver halide emulsions are more responsive to light than to X rays. The Patterson Screen Company in 1918 introduced matched intensifying screens of Kodak's first dual coated (Duplitized.RTM.) radiographic element. An intensifying screen contains a phosphor which absorbs X radiation and emits radiation in the visible spectrum or in an adjacent spectral region-i.e., the ultraviolet or infrared.
A significant recent advance in screen pairs for use with dual coated radiographic elements is represented by Luckey et al U.S. Pat. No. 4,710,637, which taught the use of an asymmetric intensifying screen pair. When a front screen exhibiting a higher modulation transfer factor (MTF) profile than had been previously realized in the art was paired with a conventional back screen, superior overall peformance, judged on a combination of image sharpness and speed, was observed. The high MTF profile requirement placed on the front screen restricted its effective thickness. X radiation absorption by the front screen was also restricted so that the imaging speed of the screen-film combination was reduced too much to permit the front screen to be employed alone. However, by employing a back screen with greater X radiation absorption capabilities and capable of satisfying a specified, though lower, MTF profile, the loss in speed attributable to the front screen was offset to an extent sufficient to observe an imaging advantage, taking both speed and sharpness into consideration.
Other prior art having some non-cumulative pertinence to one or more of the individual elements of the invention is discussed in the Appendix to the specification.